Transverse Instabilities of Coasting Beams with Space Charge

Transverse beam stability is strongly affected by the beam space charge. Usually it is analyzed with the rigid-beam model. However this model is only valid when a bare (not affected by the space charge) tune spread is small compared to the space charge tune shift. This condition specifies a relatively small area of parameters which, however, is the most interesting for practical applications. The Landau damping rate and the beam Schottky spectra are computed assuming that validity condition is satisfied. The results are applied to a round Gaussian beam. The stability thresholds are described by simple fits for the cases of chromatic and octupole tune spreads.Comment: 6 pages, 2 figures, accepted by Phys. Rev. ST - Accel. Beam

Beam dynamics in a spectrometer for the polarized positron production experiment

The proposed experiment E-166 at SLAC is designed to demonstrate the possibility of producing longitudinally polarized positrons from circularly polarized photons to be used in future Linear Collider. The experimental set-up utilizes a low emittance 50 GeV electron beam passing through a helical undulator in the Final Focus Test Beam line of the SLAC accelerator. Circularly polarized photons generated by the electron beam in the undulator hit a target and produce electron-positron pairs. The purpose of the post-target spectrometer is to select the positron beam and to deliver it to a polarimeter whilst keeping the positron beam polarization as high as possible. This paper analyzes positron transmission and polarization in the E-166 spectrometer experiment. The positron transmission has a maximum value of 7% for a positron beam energy of 5.5 MeV, while positron polarization is approximately 60%

Core-halo issues for a very high intensity beam

The relevance of classical parameters like beam emittance and envelope used to describe a particle beam is questioned in case of a high intensity accelerator. In the presence of strong space charge effects that affect the beam differently following its density, the much less dense halo part behaves differently from the much denser core part. A method for precisely determining the core-halo limit is proposed, that allows characterizing the halo and the core independently. Results in 1D case are given and discussed. Expected developments extending the method to 2D, 4D, or 6D phase spaces are examined